Differential Scanning Calorimetry Explained Quiz Thermal Analysis

1. What is the primary property measured in Differential Scanning Calorimetry

Change in mass

Heat flow difference

Light absorbance

Magnetic susceptibility

DSC measures the difference in the amount of heat required to increase the temperature of a sample and a reference. This allows scientists to detect physical transitions like melting or glass transitions.

Explanation

DSC measures the difference in the amount of heat required to increase the temperature of a sample and a reference. This allows scientists to detect physical transitions like melting or glass transitions.

2. In a DSC experiment what is the purpose of the reference pan

To hold extra sample

To act as a blank for comparison

To heat the furnace

To measure pressure

The reference pan is usually an empty aluminum pan. By comparing the heat flow to the sample pan against the empty reference pan the instrument can isolate the thermal behavior of the sample itself.

Explanation

The reference pan is usually an empty aluminum pan. By comparing the heat flow to the sample pan against the empty reference pan the instrument can isolate the thermal behavior of the sample itself.

3. A process that releases heat into the surroundings is called _____ and appears as a peak in a specific direction on a DSC curve

Exothermic processes like crystallization or curing release energy. Depending on the instrument settings these appear as peaks pointing either upward or downward on the DSC trace.

Explanation

Exothermic processes like crystallization or curing release energy. Depending on the instrument settings these appear as peaks pointing either upward or downward on the DSC trace.

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4. The glass transition temperature Tg is a sharp peak on a DSC curve

True

False

Unlike melting which is a sharp peak the glass transition appears as a step like shift in the baseline. It represents a change in the heat capacity of an amorphous material as it moves from a brittle state to a rubbery state.

Explanation

Unlike melting which is a sharp peak the glass transition appears as a step like shift in the baseline. It represents a change in the heat capacity of an amorphous material as it moves from a brittle state to a rubbery state.

5. Which of the following thermal events are endothermic in a DSC scan

Melting

Boiling

Crystallization

Glass transition

Melting and boiling require the input of energy to break intermolecular forces making them endothermic. Crystallization releases energy as bonds form making it exothermic. The glass transition is a change in heat capacity not a latent heat event.

Explanation

Melting and boiling require the input of energy to break intermolecular forces making them endothermic. Crystallization releases energy as bonds form making it exothermic. The glass transition is a change in heat capacity not a latent heat event.

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6. What does the area under a melting peak on a DSC curve represent

The melting temperature

The enthalpy of fusion

The sample mass

The heating rate

The integrated area of the peak is directly proportional to the total energy absorbed or released during the transition. For melting this value is the enthalpy of fusion which is used to calculate the crystallinity of polymers.

Explanation

The integrated area of the peak is directly proportional to the total energy absorbed or released during the transition. For melting this value is the enthalpy of fusion which is used to calculate the crystallinity of polymers.

7. The temperature at which a polymer begins to soften and become flexible is known as the _____ transition

Melting

Boiling

Glass

Sublimation

The glass transition Tg is a critical property for materials science. It determines the usable temperature range for plastics and rubbers ensuring they are not too brittle or too soft for their intended application.

Explanation

The glass transition Tg is a critical property for materials science. It determines the usable temperature range for plastics and rubbers ensuring they are not too brittle or too soft for their intended application.

8. In DSC both the sample and reference are maintained at the same temperature throughout the scan

True

False

The core principle of power compensated DSC is to vary the power supplied to the heaters so that the sample and reference temperatures stay identical even when the sample is undergoing a phase change.

Explanation

The core principle of power compensated DSC is to vary the power supplied to the heaters so that the sample and reference temperatures stay identical even when the sample is undergoing a phase change.

9. Why are DSC experiments usually conducted under a flow of Nitrogen gas

To make the sample explode

To prevent oxidation of the sample

To increase the pressure

To change the sample color

Many organic materials will burn or oxidize if heated in the presence of oxygen. An inert nitrogen atmosphere ensures that the thermal transitions observed are due to internal changes and not chemical reactions with the air.

Explanation

Many organic materials will burn or oxidize if heated in the presence of oxygen. An inert nitrogen atmosphere ensures that the thermal transitions observed are due to internal changes and not chemical reactions with the air.

10. Which factors can influence the results of a DSC measurement

Heating rate

Sample mass

Particle size

The brand of the computer

Faster heating rates can shift peaks to higher temperatures. Sample mass and contact with the pan change the thermal conductivity and the resolution of the resulting peaks.

Explanation

Faster heating rates can shift peaks to higher temperatures. Sample mass and contact with the pan change the thermal conductivity and the resolution of the resulting peaks.

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11. A DSC curve that shows a sudden drop in heat flow followed by a return to the baseline indicates an _____ event

Exothermic

Endothermic

Isobaric

Isentropic

An endothermic event like melting requires extra heat to be pumped into the sample to keep up with the reference. This creates a characteristic dip or peak in the heat flow versus temperature plot.

Explanation

An endothermic event like melting requires extra heat to be pumped into the sample to keep up with the reference. This creates a characteristic dip or peak in the heat flow versus temperature plot.

12. DSC can be used to determine the purity of a pharmaceutical drug

True

False

Impurities cause the melting peak of a substance to become broader and shift to a lower temperature. By analyzing the shape of the melting curve chemists can calculate the mole percent of impurities present in a sample.

Explanation

Impurities cause the melting peak of a substance to become broader and shift to a lower temperature. By analyzing the shape of the melting curve chemists can calculate the mole percent of impurities present in a sample.

13. What is the typical unit for heat flow on a DSC thermogram

Grams

Milliwatts

Degrees Celsius

Joules

Heat flow is a measure of power representing energy per unit time. Milliwatts are used to show the subtle changes in energy absorption or release as the sample is heated at a controlled rate.

Explanation

Heat flow is a measure of power representing energy per unit time. Milliwatts are used to show the subtle changes in energy absorption or release as the sample is heated at a controlled rate.

14. What information can be obtained from a DSC analysis of a polymer

Degree of crystallinity

Thermal stability

Oxidation induction time

Molecular weight distribution

By comparing the enthalpy of melting to a 100 percent crystalline standard the degree of crystallinity is found. DSC also measures how long a polymer lasts in oxygen before degrading.

Explanation

By comparing the enthalpy of melting to a 100 percent crystalline standard the degree of crystallinity is found. DSC also measures how long a polymer lasts in oxygen before degrading.

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15. If a DSC scan shows a sharp peak at 150 degrees Celsius and the sample is a solid powder what is likely occurring

Boiling

Melting

Glass transition

Evaporation

Sharp peaks in solid samples during heating are characteristic of melting. Because powders have high surface areas the transition is usually well defined allowing for an accurate determination of the melting point.

Explanation

Sharp peaks in solid samples during heating are characteristic of melting. Because powders have high surface areas the transition is usually well defined allowing for an accurate determination of the melting point.